A sprawling underground marijuana farm was discovered on Monday in an abandoned line of Rome’s subway. The record bust in the heart of Italy’s capital was apparently produced by sophisticated cultivation systems.

Some 340 kilograms of marijuana, with an estimated market value of over 3 million Euros, have been seized by Rome’s Financial Guard. The officers also discovered a trove of high-end agricultural equipment, including the irrigation systems and artificial lighting necessary for the farm.

According to the local media reports, the officers noticed a strong smell of marijuana during a routine inspection of an underground mushroom farm.

While the first section of the tunnel was used for growing mushrooms, a hinge mechanism in what looked like a solid stone wall revealed a hidden facility. Officers discovered a greenhouse with a highly effective cultivation system inside the first room. The hothouse was equipped with halogen lamps and a complex irrigation system consisting of water and pressure tanks, and a network of capillary tubes.

A second room was equipped with tables and the tools needed for drying, cutting and packing marijuana.

Some of the 1,000-plus plants were already packed in vacuum-sealed bags, ready for street distribution. The rest of the crop had yet to fully mature, ranging from small sprouts to meter-high plants. The manufacturers had recorded the amount of fertilizer needed for each batch on a blackboard in the corner.

The facility was also equipped with an alarm system, La Republica Roma reported. A handful of fiberglass disks were placed in the corridor leading to the greenhouse, which made a loud noise when stepped on.

The subway tunnel, located underneath Rome’s Torpignattara district, was excavated and partially built in the 1930s. The project was later abandoned and part of the tunnel was rented out for growing mushrooms.

Police believe the facility might be a part of a larger international drug ring. Only one arrest – a 57-year-old Italian man – has been made so far. Authorities are still searching for possible accomplices.